This invention relates in general to communication systems and more specifically to methods and apparatus for increasing the dynamic range or linearity of digital to analog converters for use in such systems or others.
Digital to Analog Converters (DACs) are known. Equally well known are the problems caused by the typical DAC in terms of limited dynamic range or limited linearity. These terms are somewhat synonymous in that linearity or the degree or extent of harmonic distortion or other forms of distortion is ordinarily specified at a certain output signal level or range. Alternatively the dynamic range may be specified in terms of the level that may be achieved with a distortion level not exceeding some amount. These specifications may depend on the voltage supply that is used for the DAC.
The literature is replete with sometime extraordinarily complex techniques for increasing the SFDR or spurious free dynamic range of DACs. For example U.S. Pat. No. 6,204,783 uses feedback while U.S. Pat. No. 6,097,324 uses clipping and feed forward techniques. U.S. Pat. Nos. 4,198,622, 6,204,790, 6,198,419, and 5,894,497 all uses various forms of stacking DACs in attempts to improve linearity. One or two dB is considered a significant improvement in the field. Clearly a need exists for an elegant approach to improving range and linearity in a typical DAC.